Method of making a hydrogen flame visible



May 28, 1968 c. F. MILLER ETAL METHOD OF MAKING A HYDROGEN FLAME VISIBLEFiled Aug. 50, 1965 s RmR OLE m m W K QD mm On 2 W 5H E m a Z M w a cUnited States Patent 3,385,647 METHOD OF MAKING A HYDROGEN FLAME VISIBLECharles Frederick Miller, Anaheim, and Howard L. Spicer,

La Habra, Calif., assignors to Basic Products Corporation, a corporationof Wisconsin Filed Aug. 30, 1965, Ser. No. 483,647 4 Claims. (Cl. 431-4)ABSTRACT OF THE DISCLOSURE Hydrogen is supplied to an alcohol-hydrogentorch through a sealed container of alcohol. The amount of alcohol isthereby limited to the saturation point ofalcohol vapor in hydrogen. Theburning alcohol insures a visible hydrogen-alcohol flame.

This invention relates to a method for making a hydrogen flame visibleand, more particularly, to the imparting of visibility to a finehydrogen flame used in the cutting and balling of the ends of fine goldwire in ball bonding operations on semi-conductor devices such astransistors.

In bonding conductors to semi-conductor assemblies, such as transistors,one of the methods commonly employed is so-called ball bonding. In thismethod a fine gold wire on the order of .0007" to .003" in diameter isfed through a capillary needle and bonded by the needle to terminalposts and to conductor areas on semi-conductor wafers. After the lastbond in a connection is formed, the capillary needle is raised to exposethe wire and the wire is severed and formed into balls on its ends bypassing a fine hydrogen flame across it. When the needle is again moveddown for another bonding operation, it engages the ball on the end ofthe wire to feed the wire against the surface to which it is to bebonded and to press the ball against the surface to bond it thereto.

One of the major problems in this operation has been control of thehydrogen flame to form a uniform sized ball on the end of the wire ineach cutting operation. The size of the ball is dependent upon the sizeand character of the flame and its position relative to the wire as wellas upon the effect on the wire of inert atmosphere gas commonly used toenvelop the cutting area. However, since a hydrogen flame is invisibleits size and character could only be judged by observing its action onthe wire during a cutting and balling operation, which made adjustmentof the flame extremely diflicult.

It is accordingly one of the objects of the present invention to providea method by which the hydrogen flame is made visible so that its size,character and position relative to the wire to be out can easily beobserved and adjusted.

Another object is to provide a method in which alcohol vapor inautomatically controlled quantities is added to hydrogen being suppliedto a torch to give the flame from the torch an easily visible color.

According to a feature of the invention the hydrogen supplied to thetorch is passed through the upper part of a sealed container containingalcohol to pick up alcohol vapor. The quantity of alcohol vapor pickedup is automatically limited to the saturation of alcohol vapor inhydrogen so that the quantity is accurately and automaticallycontrolled. Furthermore, since alcohol adds only carbon to the flame, itdoes not introduce troublesome impurities which might affect the cuttingand balling operations.

The above and other objects and features of the invention will be morereadily apparent from the following description when read in connectionwith the accompanying drawing in which:

FIG. 1 is a diagrammatic view of a ball bonding apparatus illustratingonly the cutting portions of the apparatus; and

FIG. 2 is a sectional view of the alcohol container of FIG. 1.

As shown in FIG. 1 a fine gold wire indicated at 10 is to be bondedbetween a semi-conductor wafer 11 and terminal posts 12 carried by abase 13 and forming a part of a transistor assembly. As illustrated,short lengths of the wire are bonded between conductive areas on theouter face of the wafer 11 and the respective terminal posts 12 to formelectrical connections therebetween.

The operation is performed in a known type of wire bonding apparatuswhich includes a small capillary needle 14 through which the wire 10 isthreaded. When the wire 10 is cut by a flame as, for example, thehydrogen flame 15 emitted from a torch 16, the wire will be melted whereit is contacted by the flame and the ends thereof will form intogenerally spherical balls as shown at 17. These balls are larger thanthe bore in the needle 14 so that when the needle is moved down the endof the needle will engage a ball and carry the wire down until the ballis pressed against either the conductive surface on the wafer or one ofthe terminal posts 12 to be bonded thereto. After a connection has beencompleted the needle is raised to approximately the position shown andthe torch is moved so that-the flame will sweep across the wire betweenthe last bonding point and the needle to sever the wire and to causeballs to be formed on the severed ends thereof.

As shown, the torch is supplied with hydrogen from a tank 18 through asuitable pressure regulating valve 19 and a conduit 21. The torch may bemovably mounted for swinging across the wire and is carried by a portionof the wire bonding apparatus and is moved synchronously with movementof the needle or under the control of an operator to effect the severingof the wire at the desired times.

In order to impart visibility to the hydrogen flame 15 so that the size,character and position of the flame relative to the wire can readily beadjusted, the hydrogen supplied to the torch has alcohol vapor added toit according to the present invention. For this purpose a container 22is provided. As shown in detail in FIG. 2, the container comprises acylindrical wall 23 which may be welded to a base plate 24 whichpreferably extends beyound the container and is formed in its extendedarea with one or more openings 25 to receive mounting screws. The top ofthe container is closed by a flat top plate 26 welded to the upper edgeof the cylindrical wall 23 and formed with spaced conduit connections 27and 28. Preferably also a removable filler plug 29 is provided in theside wall through which alcohol may be inserted into the container to amaximum level approximately as indicated at 31.

With the container filled with alcohol and preferably with iso-propylalcohol to approximately the level 31, and with the filler plug 29secured in place to seal the container, the conduit connection 27 may beconnected to the conduit 21 leading to the hydrogen tank 18 while theconduit connection 28 is connected to a conduit 32 leading to the torch16. The conduit 21, as shown in FIG. 2, extends into the container to apoint near the bottom thereof so that hydrogen entering the containerwill be introduced below the liquid level to bubble up through theliquid thereby to insure saturation of the hydrogen with liquid vapor.The container is preferably relatively heavy to withstand any pressureswhich may develop therein during use without leakage. In use of theapparatus, the alcohol in the container will vaporize so that the upperpart of the container will be filled with alcohol vapor. As the hydrogenfrom the tank flows through the upper part of the container to thetorch, it will pick up alcohol vapor to the extent permitted bysaturation of the hydrogen by the alcohol vapor. At the flame both thehydrogen and the alcohol vapor will burn simultaneously and the alcoholvapor present is sufficient to give the flame a strong blue color whichis readily visible to the eye. Therefore, since the flame can easily beobserved, its size, character and position can easily be adjusted toperform the cutting and balling operation in the desired and mosteflicient manner.

While one embodiment of the invention has been shown and described indetail, it will be understood that this is for the purpose ofillustration only and is not to be taken as a definition of the scope ofthe invention, reference being had for this purpose to the appendedclaims.

What is claimed is:

1. The method of making a hydrogen flame from a torch visible whichcomprises supplying a stream of hydrogen to the torch to burn in a flameand adding alcohol vapor to the hydrogen stream before it reaches thetorch.

2. The method of claim 1 in which the alcohol vapor is iso-propylalcohol.

3. The method of making a hydrogen flame from a torch visible whichcomprises supplying a stream of hydrogen to the torch to burn in aflame, confining alcohol in a closed space, and passing the hydrogenstream through the closed space to pick up alcohol vapor therefrombefore the hydrogen stream reaches the torch.

4. The method of claim 3 in which the hydrogen is introduced into theclosed space below the level of the alcohol therein.

References Cited UNITED STATES PATENTS 1,325,116 12/1919 Sebilk 158-11751,718,732 6/1929 Danforth 158117.5 2,003,864 6/1935 Nock 1581l X FOREIGNPATENTS 486,170 3/1912 France.

JAMES W. WESTHAVER, Primary Examiner.

